1. Field of the Invention
The present invention relates generally to a control apparatus for an air conditioner of a motor vehicle. In particular, the invention concerns improvements in or relating to a control system for a fully automatized air conditioner adapted to automatically control temperature, quantity and the like of air to be blown into the passenger compartment of a motor vehicle.
2. Description of the Prior Art
As schematically illustrated in FIG. 1, the hitherto known air conditioner of the kind mentioned above is usually provided with an automatic control circuit 1 which is adapted to automatically control temperature and air quantity for the passenger compartment of a motor vehicle as well as the selection of air flow outlet ports and the like. Further, to cope with an emergent event such that the controlling operation of the automatic control circuit 1 fails to work there is provided an emergency circuit 2 in addition to the automatic control circuit 1 for assuring operation of at least the fundamental functions of the air conditioner, i.e. maximum heating and cooling capabilities. The failure in operation of the automatic control circuit 1 may result, for example, from a malfunction of the control circuit itself, failure of the external temperature sensor, interior temperature sensor and/or elements supplying relevant input signals to the control circuit 1. The automatic control circuit 1 and the emergency circuit 2 are arranged to be selectively changed over by means of a manipulating switch 3. In FIG. 1, reference numeral 4 denotes a power supply source such as a battery.
In the automatically controlled air conditioning system of the arrangement outlined above, the manipulating switch 3 takes the form of an integral structure with a temperature control switch 5, as is indicated by a reference symbol 3 (5) in FIGS. 2 and 3. Switch 5 inherently functions to select and preset a given temperature for the air flow produced by the air conditioner. More particularly, the manipulating switch 3 (5) is operative not only over a temperature control range T but also at emergency positions FH and FC. Describing in more concrete the structure of this switch by referring to FIG. 3, it includes a base plate 6 in the form of an annular disc 6 on which an arcuate resistance layer 7 is provided and electrically connected to the automatic control circuit 1. There are further provided, in the vicinity of the opposite ends of the arcuate resistance strip 7, emergency contacts 8H and 8C (corresponding to the emergency positions FH and FC shown in FIG. 2), respectively, which are connected to the emergency circuit 2 for assuring the maximum heating or cooling function of the air conditioner, in case of emergency (i.e. upon occurrence of the emergent conditions described above). On the other hand, a manipulating knob 9 is mounted rotatably relative to the base plate 6, and it is provided with a movable contact piece 10 which is adapted to be slidably displaced in contact with the base plate 6, as the manipulating knob 9 is revolved. When the manipulating knob 9 is operated within the temperature control range T, the movable contact piece 10 is slidably displaced on the resistance layer 7 to establish a corresponding resistance value on the basis of which the automatic control circuit 1 in turn is operated. On the other hand, when the manipulating knob 9 is set to either one of the emergency positions, that is, either the maximum heating position FH or the maximum cooling position FC, the movable contact piece 10 is brought into contact with either the emergency contact 8H or 8C to thereby permit the emergency circuit 2 to operate in the corresponding mode.
However, the foregoing conventional arrangement is disadvantageous in that there is the tendency that the emergency circuit 2 may be rendered operative, even though the operator does not intend to do so, because of the fact that the manipulating switch 3 (5) has such a structure that the temperature controlling resistance layer 7 and emergency contacts 8H and 8C are located in flush relationship with each other so that the knob 9 is liable to be excessively turned to render the emergency circuit 2 operative when it is desired to keep the automatic control circuit 1 operating.